1. Field of the Invention
The present invention relates to a focused ion beam processing method in which a focused ion beam is applied to microstructures such as new materials, semiconductor devices, photomasks, X-ray masks, storage devices, and magnetic heads for processing or observation thereof.
2. Description of the Related Art
Conventionally, to repair a transmissive photomask, the location to be repaired is irradiated with a focused ion beam for processing. To improve processability, the focused ion beam is at an energy level of about 30 keV and has a beam diameter of 30 nm or smaller for nanometer processing in a quick and highly precise manner (see, for example, JP-A-2001-6605). In recent years, however, there has been a problem that an irradiated object, such as a transmissive photomask, gets damaged through irradiation of the focused ion beam. There has been reported a problem in repairing a transmissive photomask, that is, ions of the focused ion beam that penetrate a transmissive layer (SiO2, for example) during irradiation reduce the transmittance of irradiation light to be applied in a transfer process. In a mask process in semiconductor manufacturing, there has been proposed a method, as one of the solutions to this problem, in which the surface processed by the focused ion beam is washed to remove the damaged transmissive layer with a depth of 25 nm or deeper from the surface. According to this method, as shown in FIG. 7, it has been reported that 97% or greater of transmittance of the transmissive photomask after repair can be obtained for the laser light with a wavelength of 248 nm or greater, which has been conventionally employed in the transfer process, under a standard operating range (the number of scans is ten) (see, for example, Ryoji Hagiwara et al., Proc. of SPIE, “Advanced FIB mask repair technology for ArF lithography”, (USA), 2001, No. 4069, page 555). Thus, a transmissive photomask is repaired with a focused ion beam and used in a patterning process for a linewidth of 90 nm or greater that can be transferred by laser light with a wavelength of 248 nm or greater.
In recent years, as the size of structures in semiconductor manufacturing has been increasingly reduced, developments of photolithography technologies for transferring linewidth in a range less than 90 nm are being pushed forward and studies are being carried out to investigate the use of laser light with a wavelength shorter than 248 nm (for example, 193 nm-laser light emitted from a medium made of ArF) as laser light to be applied. However, according to the non-patent document 1, as shown in FIG. 7, the above-mentioned method for repairing a transmissive photomask does not contribute to sufficient improvement in transmittance of laser light with a wavelength less than 248 nm, and the repaired portion may unfortunately be transferred in the transfer process in semiconductor manufacturing. Even when laser light with a wavelength of 248 nm or greater is used, the removal of the damaged portion of 25 nm or greater by washing reduces the thickness of the transmissive layer, resulting in a change in phase angle of applied laser light by 20 degrees or greater. Consequently, in a phase-effect mask utilizing a phase effect, mutual laser light interference unfortunately reduces the intensity of applied laser light. Such a problem of damaged portion formation due to a focused ion beam also applies to a reflective mask in which irradiation light (EUV) is reflected for the purpose of transfer. That is, when an absorption layer of a reflective mask is repaired with a focused ion beam, the reflectance of a reflection layer is unfortunately reduced.
The invention has been made in view of above situations and provides a focused ion beam processing method in which the surface of a workpiece is irradiated with the ion beam and processed with minimum damage to the workpiece.